"Well," remarked Frank, as he prepared to settle down again into his snug blanket, "I reckon we're not going to be scared away by a little thing like that growl. Unless we hit a snag, or Peg Grant and his guides break up our game, a few days ought to see us heading back to Circle Ranch with a story calculated to make the boys sit up and take notice; or else——"
"Just pull up right there, Frank," interrupted his chum, with a laugh. "There's nothing going to happen to knock us out. If that same Peg comes around, making a nuisance of himself, why, he's due for a nice little surprise, mark me. Besides that; what could there be to make trouble?"
"Oh, I'm not bothering my head over it, Bob," declared the other, as he dropped into the nest he had made in his blanket. "But say, did you take notice of the way our horses acted while that thing was going on?"
"Just what I did," the other replied. "They must have been trembling all over. I could hear your Buckskin snorting to beat the band, and pawing just like he does when he's worried. Reckon they didn't know what to make of it, either, seeing that there's nary a sign of a storm cloud around. But both horses have quieted down again. They think all danger of a howler has passed away."
Frank made no reply. He was already getting ready to resume his interrupted nap; and Bob lost no time in following his example, both confident that in the alert Buckskin they had a sentry capable of giving ample warning should peril threaten.
Once more Frank composed himself for sleep. The many noises of the night, which had seemed to cease while that mysterious rumbling was going on in the heart of the lofty mountain, had again resumed sway. The hum of insects; the melancholy hooting of the lonely owl, in some willow or cottonwood tree near the base of the mountain; the far-off howl of the prairie wolf; or the more discordant voice of the skulking coyote—all these things were as familiar music in the ears of the boy whose cradle had been the rich black earth of the grazing country ever since he was old enough to remember anything.
They all did their share in lulling him to sleep. And, no doubt in dreams, he was once more galloping across the wide prairie on the back of his mount, his nostrils filled with the life-giving air of the sage-covered level.
Frank slept, he never knew just how long.
This time it was not the rumbling sound and the fearful vibration of the ground that aroused the two saddle boys; but a far different cause.
When Bob sat up he found his comrade already erect, and apparently listening as though keenly alive to some approaching peril.